When the four of us were kids we did a lot of teasing and my oldest brother would give us nicknames and then shorten them to initials so we knew what he meant, but it was private. I can't (or, won't) say here what ICBB or BSIS stood for, but it was all good fun. I had my own initials for my big brother.
Here is a poem I wrote about him years ago. He is still my hero...
My BBB
About seven years my senior,
He's 'My Big Brother Bill'.
A source of awe; of strength and love
Since I was just a pill.
He's big & rough & tough & gruff,
But his heart is purest gold,
My admiration and respect
He will forever hold...
And he can do most anything;
There's not much he doesn't know.
He's confident, but not too proud,
If he doesn't know; he'll tell you so.
I'm so proud to be his sister
And though I know it's plain to see,
